So Casper has a really bad case of guarding his toys, but only towards other dogs. Any human can come by and take the toy but the moment another dog even thinks about touching a toy that's nowhere near him he loses his shit and runs towards the dog barking and growling and will even try to attack the other dog (unless its bigger than him).
He did this in his puppy class to the point where he was not allowed to play in the play sessions and the teacher just said to keep him away from dogs while there are toys around (which I think is really stupid advice).
Any advice would be appreciated

The best thing you can do, don't give him, or let the others have toys when they play together. Toy guarding is a serious issue, there are a few ways to stop it. However I advise you to seek a professional behavioural specialist. That way they can help you see signs and warnings, learn to correct them.

As I said, until you seek help from someone in real life, don't let him play with toys if other dogs are around.

I can't let Okami have antlers/bones around other dogs... she guards them. She also water guards, so at the dog park I have to play water goalie while she drinks... it is ridiculous, I know. It keeps her and everybody else safe though. She has never acted badly, she just growls, which is my warning sign to correct/take away.